The present invention relates to passive infrared motion detectors of the type used in residential outdoor lighting fixtures, for example, to illuminate a walkway or driveway when a person or automobile approaches. The invention is more particularly directed to arrangements for making the motion detector an inconspicuous element of the lighting fixture and to a mirror arrangement suitable for use in such motion detectors.
Lighting devices that automatically turn on a light when a person or a motor vehicle approach have been known for some time. A popular form of such device is responsive to infra-red radiation emitted by a person or motor vehicle as the person or vehicle moves within the field of view of the device. These devices are generally referred to as passive infra-red, or xe2x80x9cPIR,xe2x80x9d motion detectors and light fixtures.
The first PIR motion detectors were not used with light fixtures at all, but were used in surveillance and alarm systems to monitor for intruders. They were stand-alone devices and tended to be large and bulky in appearance. They employed assemblies of germanium lenses or multi-faceted mirrors or combinations of mirrors and lenses to direct infra-red radiation from an object moving in the field of view to a PIR sensor. The first commercial PIR motion detectors for activating lights were used with utilitarian lighting such as flood lights or other area lighting. Although the motion detectors were bulky and quite conspicuous, that was not seen as a significant drawback in view of their utility in activating the lights in response to intruders. Examples of early PIR motion detectors employing lenses, mirrors and various combinations may be seen in U.S. Pat. Nos. 3,631,434 and 3,958,118 to Schwarz; 3,703,718 to Berman; 3,928,843 to Sprout et al.; 3,988,726 to Reiss et el.; and 4,268,752 to Herwig et al.; and various patents cited therein.
Later, utilitarian PIR light fixtures appeared in which the mirrored optics and germanium lens optics were replaced with plastic Fresnel lens optics. A Fresnel lens of the sort used in connection with motion detectors comprises a thin sheet of flexible plastic material that permits infra-red radiation to pass through it and on which are formed a number of individual Fresnel lens segments or lenslets. See for example U.S. Pat. No. 3,203,306 to Lefferts for an individual Fresnel lens segment formed on such a plastic sheet and U.S. Pat. Nos. 4,321,594 to Galvin or 4,703,171 to Kahl et al. for a segmented Fresnel lens having a plurality of lens segments side-by-side on a plastic sheet. The segmented Fresnel lens was considerably simpler and less expensive to manufacture than the previously employed mirror or germanium lens arrangements and permitted the motion detector units to be made considerably more compact. The flexible plastic sheet on which the lens segments were formed occupied little volume and could be supported with a simple bracket structure at the edges of the sheet with no need for additional brackets to support the individual lens segments. Moreover, the plastic sheet could be bent into a semi-cylindrical or similar curved shape to position the individual lens segments more or less uniformly about the PIR sensor. With the introduction of the flexible plastic segmented Fresnel lens, the earlier lens and mirror arrangements were eschewed in favor of new Fresnel lens arrangements, which were more compact, inexpensive, lightweight, and generally easier to work with.
With the sheetlike segmented Fresnel lens PIR motion detectors could be made considerably less obtrusive, and they were soon added to decorative light fixtures as well as utilitarian ones. At first the motion detector was located in a small housing mounted on an intermediate backplate, which was mounted on a wall over an electrical junction box, and to which the decorative lighting fixture, in turn, was mounted. Such a backplate-mounted motion detector is illustrated in FIG. 1 of U.S. Pat. No. 5,590,953 Haslam et al. This arrangement became commercially feasible because of the segmented Fresnel lens, which permitted the motion detector housing to be sufficiently compact that it lessened the distraction from the decorative nature of the lighting fixture.
In recent years the trend has been to incorporate the motion detector within the decorative light fixture itself to make it less obtrusive either by concealing it altogether or at least by giving it a decorative appearance so that it does not detract appreciably from the ornamental style of the light fixture. Examples of PIR lighting fixtures that endeavor either to conceal the motion-detecting unit or to embellish it so as to enhance its decorative appearance may be seen in U.S. Pat. Nos. 5,282,118 and 5,434,764 to Lee et al.; 5,575,557 and Des. 382,082 to Huang et al.; 5,590,953 to Haslam et al.; and 5,626,417 to McCavit.
When the motion-detecting unit is incorporated into the body of a decorative light fixture, the flexible plastic lens is generally formed to be a part of a wall of some portion of the fixture and may be tinted to blend in with the fixture body. Thus, in FIG. 2 of U.S. Pat. No. 5,590,953 the segmented Fresnel lens forms part of a cylindrical wall and in FIG. 3 of the same patent it is shaped to form a portion of a conical wall. This construction imposes a limitation on the lens optics. In decorative fixtures the nature of the fixture bodyxe2x80x94its curvature, slope, profile and overall shapexe2x80x94is chosen primarily by aesthetic considerations to give the fixture its decorative appearance and to some extent by manufacturability considerations to maintain a lower cost. The resulting fixture body design, however, then constrains the optics of the segmented Fresnel lens, which will generally follow the contour of a wall of the fixture body. That is, the Fresnel lens may be disposed in a fixture wall at an angle or as part of a curved surface so as to impair the ability of the lens to focus radiation from a desired direction on the sensor. Alternatively, the aesthetic design of the light fixture may be compromised so as to provide a more favorable optical environment for the segmented Fresnel lens. In one attempt to circumvent this problem, U.S. Pat. No. 5,626,417 provides a window in the fixture wall with a plastic cover and places the segmented Fresnel lens in a cylindrical optical disposition inside the fixture behind window.
Meanwhile another trend has been to provide decorative fixtures with longer range and wider fields of view to cover the many arrangements in which the fixture may be mounted by a front door or driveway. This makes greater demand on the optics of the segmented Fresnel lens at the same time that the ornamental requirements on the lighting fixture constrain the feasible optical arrangements of the lens.
The present invention provides a motion detector assembly for a decorative lighting fixture that conceals or disguises the presence of the motion detector in a decorative element that may be integrated in a natural and graceful manner into the design of the lighting fixture without the limitations on design imposed by the use of the segmented Fresnel lens.
Briefly, a lighting fixture according to the invention includes a motion detector housing that is shaped to have a decorative external appearance harmonious with the style of the lighting fixture and forming an integral part of the lighting fixture. The decorative housing is formed with an aperture for admitting infra-red radiation into the housing from the monitored field of view. An aperture cover extends over the aperture to protect the interior and to conceal the presence of the aperture. The aperture cover is transmissive to infra-red radiation and generally conforms to the shape of the housing in the vicinity of the aperture so as to conceal the presence of the aperture. Mounted within the decorative housing are a passive infra-red (PIR) sensor and a mirror assembly that directs infra-red radiation from the field of view to the sensor. The mirror assembly comprises a plurality of mirror faces that define a plurality of monitored zones in the field of view. Each respective mirror face defines an optical path in which radiation admitted through the aperture from an associated zone is directed to the sensor solely by the respective mirror face. That is to say, the optical paths are defined by the mirror assembly alone with only a single reflection taking place for each optical path, and it is not necessary to employ secondary mirrors or auxiliary lenses to complete the optical path. Notwithstanding the absence of secondary mirrors or auxiliary lenses, the motion detector remains sufficiently compact that it may be comfortably hidden in a decorative element with little or no compromise in the artistic aspects of the decorative element. Moreover, the mirror faces may be arranged to direct radiation to the sensor from zones positioned at two or more vertical levels of view in the lighting fixture""s field of view and to provide a wide-angle field of view so that there need be little or no compromise in the utilitarian aspects of the motion detector. In this way the motion detector does not depend on the use of Fresnel lenses and thereby avoids any limitations and deficiencies of the plastic segmented Fresnel lens, yet the motion detector does not require that the aesthetic design of the lighting fixture be compromised. In fact, since the aperture cover is only provided for protection and/or concealment and plays no optical role in the operation of the motion detector, the lighting fixture designer is given more freedom in the development of aesthetic designs, and the motion detector arrangement of the present invention may be incorporated into more intricate or complex designs than is otherwise feasible with the prior art where the aperture cover must also carry an array of Fresnel lenslets.
The mirror assembly may be specially arranged according to the invention to achieve a field of view that is wide angle and at the same time has at least two vertical levels of view. The mirror assembly has a first section that defines a first tier of side by side mirror faces terminating in distal extremities. The infra-red sensor is positioned in front of the mirror assembly, and the mirror faces are formed and disposed to direct infra-red radiation to the sensor from a first laterally extending region in the field of view of the motion detector. The distal extremities and the sensor are arranged so that a ray path emanating from a zone at the lateral reaches of the first region in the field of view passes beneath a first distal extremity of the tier and reflects off the mirror face at the other distal extremity to the sensor. In this manner the tier of mirror faces is able to define a field of view in the direction of the first region having an angular width of at least 160 degrees and, depending on the length and shape of the tier and angular configuration of the distal extremities, extending at least up to 220 degrees.
By way of summary, it is an object of the invention to provide a small unobtrusive motion detector housing for use with a decorative lighting fixture that avoids the use of the customary sheetlike segmented Fresnel lens. It is a further object of the invention to provide a motion detector housing that is decorative in appearance and that conceals or disguises the presence of the motion detecting apparatus. It is a further object of the invention to provide a motion detector housing arrangement with disguised or concealed motion detecting apparatus that is easily adaptable to a variety of decorative configurations so as to give a degree of freedom to the aesthetic designer to design the outward shape and appearance of the housing without unduly constraining the optical arrangement of the motion detector. It is yet a further object of the invention to provide an unobtrusive decorative motion detector housing with concealed or disguised motion detector apparatus that nevertheless provides a wide field of view (at least 160 degrees) and a plurality of vertical levels of view.